Contributions to the biology and ecology of Petrolistes armatus (Anomura, Porcellanidae).

In an experimental study, P. armatus survived a wide range of salinities (6- 33 ppt.) and the three experimental temperatures (15, 23, and 30 degrees) fairly well after 96 hours exposure. Slightly higher mortality (35%) was produced by the 6 ppt, 23 degree condition. Generally 15 C produced the highest mortalities. When the exposure period was extended to seven days an increase in mortality from 35 to 53% occurred at the 6 ppt, 23 C condition. Only slight increases in mortality occurred at the other conditions, mostly at 15 C. P. armatus was a good osmoregulator at 23 C between 8 and 18 ppt. Between 18 and 33 ppt the blood conformed more closely to the osmotic concentration of the medium until it was nearly isosmotic at 33 ppt. This animal was a good volume regulator between 8 and 33 ppt. Temperature did not significantly affect volume regulation except at the 15 and 30 C conditions. At 15 C an increase in percent body water occurred at 8 ppt and a decrease occurred at 18 ppt. At 30 C a decrease in percent body water occurred at 33 ppt. The values of percent body water at the other condtions were not significantly different from each other. The feeding behavior of this crab was similar in most aspects to that described for other members of the family Porcellanidae. The primary method of feeding was filtering plankton out of the water with the third maxillipeds. P. armatus also supplements its plankton diet by scraping algae off of rocks and shells and by scavenging on dead animals.